In the past few decades, the in situ sustained drug delivery platforms present fascinating potential in sentinel chemotherapy of various solid tumors. In this work, doxorubicin (DOX), a model antitumor drug, was loaded into the thermogel of poly(lactide-co-glycolide)-block-poly(ethylene glycol)-block-poly(lactide-co-glycolide). The moderate mechanical property of DOX-loaded hydrogel was confirmed by rheological test. In vitro degradation revealed the good biodegradability of thermogel. The DOX-loaded hydrogel exhibited the sustained release profiles up to 30days without and even with elastase. The improved in vivo tumor inhibition and reduced side-effects were observed in the DOX-incorporated hydrogel group compared with those in free DOX group. The excellent in vivo results were further confirmed by the histopathological evaluation or terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. The thermogel with great prospect may be used as an ideal controlled drug delivery platform for the designated and long-term antitumor chemotherapy.